Preheat the oven to 350°F. Grease three 9-inch round cake pans, line the bottoms with parchment, then grease the parchment and lightly dust the pans with cocoa powder.

Whisk the flour, sugar, cocoa powder, baking soda, baking powder, and salt in a large bowl. Add the eggs, buttermilk, oil, and vanilla, then beat until the mixture is smooth.

Slowly pour in the boiling water while mixing on low speed. The batter will be thin, which is expected and helps create a moist cake.

Divide the batter evenly among the prepared pans. Bake for 25 to 30 minutes, or until a toothpick inserted in the centers comes out with a few moist crumbs.

Cool the cakes in their pans for 10 minutes. Turn them onto wire racks, remove the parchment, and cool completely before frosting.

For the frosting, whisk the evaporated milk, egg yolks, brown sugar, granulated sugar, and butter in a medium saucepan. Cook over medium heat, stirring constantly, for 10 to 12 minutes, until thick enough to coat a spoon.

Remove the saucepan from the heat and stir in the vanilla, coconut, and toasted pecans. Transfer the frosting to a bowl and cool until spreadable.

Place one cake layer on a serving plate. Spread one-third of the frosting over the top, leaving the sides mostly uncovered, then repeat with the remaining layers and frosting.

Let the assembled cake stand for 30 minutes before slicing. Serve at cool room temperature for the softest cake and creamiest frosting.